. 2006 Aug 7;62(3):260–264. doi: 10.1136/thx.2005.056333

Table 4 Crude risk ratios (RR) of developing two or more respiratory symptoms according to decreasing degree of AHR compared with subjects with PC₂₀ >32 mg/ml.

Airway responsiveness (PC₂₀) threshold values (mg/ml)	Cumulative†
Airway responsiveness (PC₂₀) threshold values (mg/ml)	Subjects with incident respiratory symptoms n (%)	RR (95% CI)
⩽4	9 (47.4)	30.4 (9.9 to 93.0)***
⩽8	13 (34.2)	17.6 (6.8 to 45.1)***
⩽16	27 (36.5)	19.4 (8.6 to 43.8)***
⩽32	35 (30.4)	14.8 (6.8 to 32.0)***
>32	9 (2.9)	1

AHR, airway hyperresponsiveness; PC₂₀, concentration of methacholine provoking a 20% fall in FEV₁; RR, risk ratio; CI, confidence interval.

***p<0.001; subjects with PC₂₀ >32 mg/ml considered as reference category.

†p<0.001 for whole group (Cochran‐Armitage tests for trend in RR applied to mutually exclusive categories of AHR).

Table 4 Crude risk ratios (RR) of developing two or more respiratory symptoms according to decreasing degree of AHR compared with subjects with PC20 >32 mg/ml.